Cosmic microwave background (CMB) anisotropy is our richest source of
cosmological information; the standard cosmological model was largely
established thanks to study of the temperature anisotropies. By the end of the
decade, the Planck satellite will close this important chapter and move us
deeper into the new frontier of polarization measurements. Numerous
ground--based and balloon--borne experiments are already forging into this new
territory. Besides providing new and independent information on the primordial
density perturbations and cosmological parameters, polarization measurements
offer the potential to detect primordial gravity waves, constrain dark energy
and measure the neutrino mass scale. A vigorous experimental program is
underway worldwide and heading towards a new satellite mission dedicated to CMB
polarization.Comment: Review given at TAUP 2005; References added; Additional reference